1. Field of the Invention
This invention relates to apparatus for delivering a volume of air over a given zone, and more particularly relates to a conduit for directing air flow across high voltage A.C. discharge electrodes in order to direct a stream of ionized air over remotely positioned charged objects for the purpose of effecting neutralization thereof.
In order to determine the ability of ionized air blowers to neutralize a charge in a given location, one generally measures the conductivity of the air or the ion concentration with respect to the mobility thereof. Following recent standards developed for protection of electrostatic discharge susceptible items through ionization (EOS/ESD Standard No. 3, dated September 1987) evaluation of the efficiency of an ionizer or an ionization system is accomplished by directly measuring the rate of charge decay of articles placed in a zone extending to a predetermined depth in front of the ionizing system and transversely positioned with respect to the centerline thereof. "EOS/ESD" refers to Electrostatic Overstress/Electrostatic Discharge Association, of 200 Liberty Plaza, Rome, N.Y. 13440. According to EOS/ESD Standard No. 3, a charged plate monitor can be constructed with an insulated metal test plate having dimensions of six inches by six inches and electrically isolated from ground. The metal test plate must have a capacitance of 20 picofarads when measured with respect to ground. The charged plate monitor can be used to determine the relative ion concentration in a given location.
The EOS/ESD Standard No. 3 directs testing of table top ionized air blowers by using a test pattern where the test points are arranged in a pattern of four rows and three files in front of the ionizer to be tested. Each file is positioned three abreast from a centerline directly before the ionizer and spaced from each other by a center-to-center distance of twelve inches. A plan view of the test area is set forth in FIG. 5.
The charged plate monitor is placed sequentially at each test point. At each test point, the plate is charged to 1,000 volts, the plate being monitored by coupling to an electrometer (or by measuring the field by a non-contacting field meter). The decay time ( a measure of neutralization efficiency) is assessed by determining how long it takes the test plate to reach 100 volts at each test point.
2. Prior Art
In U.S. Pat. No. 3,844,657, a large volume of air is forced by a blower or fan through a chamber having a high efficiency particulate filter at the exit end thereof so that the air is squeezed through the particulate in laminar flow disposition. An area static eliminator is oriented about the outlet of the system to cause the positive and negative ions emitted from the discharge electrodes thereof to sweep in a laminar air flow path over a contact printing surface and cleanse the latter of charged particles. The pattern of the air flow shown by this patent is basically linear and coextensive with the width of the outlet. No vanes or other means are disclosed for diverting the laminar flow laterally so as to provide transverse expansion of the field of ionization.
U.S. Pat. No. 4,417,293 shows a nozzle in which a compressed gas is passed through an orifice having high voltage discharge electrodes adjacent the open end. After expansion through the nozzle orifice, the aerosol created entraps air ions within frozen microparticles allowing them to be discharged over a wider area for purposes of static neutralization.
In Model VSE 3000 air ionizer made by Chapman Electrostatic Systems, of Portland, Me., air is diverted laterally by wide angle diffuser vanes and then blown over discharge points to widen the field traversed by the dual polarity ions.
3. Objects of the Invention
One of the problems caused by diverter vanes is the production of back pressure as the blower or fan internally directs the air stream against the facing vane surfaces and causes turbulence in the air flow during the emergence from the ionizer. In all cases where diverter vanes are employed in various attitudes, it has been found that the charged plate monitor of EOS/ESD Standard No. 3, Ionization, exhibits disappointing results for decay times in those test point areas located laterally of the centerline.
It is therefore an object of this invention to provide an ionized air blower system in which air ions will be distributed uniformly over a widened lateral area without detracting from neutralization in a forward direction.
Another object of this invention is to provide an air distribution system, especially for extended range static eliminators, wherein turbulence in the air pattern will be minimized and the field of neutralization effective over a widened forward and transverse area.
Still another object of this invention is to provide an extended range static eliminator in which the configuration of the conduit containing the air flow is the primary source for directing the air ions over an uniform expanded path.
Other objects of this invention are to provide an improved device of the character described which is easily and economically produced, sturdy in construction and highly efficient and effective in operation.